High Harmonic Imaging of Few-Cycle Laser Pulses

We show that the strength of the central electric field peaks in a few-cycle laser pulse can be recovered from a frequency-time image of the high harmonic spectrum generated in a gas volume. Pulse intensity, duration, and also the carrier-envelope phase ${\phi }_{\mathrm{C}\mathrm{E}}$ can be determined. A simple and robust observable is defined that provides a gauge of ${\phi }_{\mathrm{C}\mathrm{E}}$ for pulse durations up to three optical cycles, corresponding to 7.8 fs FWHM at the Ti:sapphire wavelength of 800 nm.